<p>The high ductility of Mg has posed major challenges for nanofabrication utilizing mechanical ball-milling. While the addition of organic solvents is effective, it has been unclear how they improve the ball-milling effect by modifying the material’s surface properties. Herein, we report that the solvent-mediated partial ionicity plays an important role in enhancing the nanosizing effect of Mg_87.5Ni_5.5Y₇ alloy. This approach enables the Mg_87.5Ni_5.5Y₇ particles to be 88 times smaller than those of the solvent-free procedure. The Mg_87.5Ni_5.5Y₇ nanoparticles underwent complete dehydrogenation in 3 min at 300 °C and in 17 min at 240 °C, which can be stably cycled at least for 500 times. Solvent (THF) adsorption on Mg induces Mg^δ⁺‒Mg^δ− dipole structure. This increases the surface hardness of Mg-based alloy and maximizes the ball milling-driven structural deformation, thereby facilitating ion migration. Mg‒Mg bond breaking is caused by the resulting Coulombic repulsion between Mg atoms. These findings provide an affordable approach for nanoparticle fabrication of highly ductile materials.</p>